Effect of generator saturation on shaft torques during faulty synchronization

Abstract

Torque developed during a short circuit of an alternator is considered as the most severe case for the design of the shaft by engineers. But studies show that shaft torque during a faulty synchronization may exceed the torque developed during a short circuit at certain conditions. Accurate prediction of the shaft torque in faulty synchronization process is therefore important in the design stage to ensure the safe operation of ac generators. In the reported simulations the effects of saturation is either neglected or taken into consideration in the form of mutual path saturation only. The procedure may provide underestimated values of shaft torque because the current involved in such a situation may become significantly high at certain synchronizing angle. Hence, simulations should consider leakage path saturation during shaft torque evaluation particularly during short circuits and faulty synchronization. This paper describes a method of simulating faulty synchronization of a generator to a power system considering a detail generator model in mathematical and state space form. A method of incorporating saturation effects both in the mutual and leakage path is proposed. Simulations have been carried out for different synchronizing angles to evaluate the instantaneous and the peak shaft torques with and without saturation effects. Finally, a typical comparative study between faulty synchronization and short circuit faults of ac generators is provided in this paper, where, the results of faulty synchronization conditions were evaluated by proposed simulation method presented in this paper.